The use of polyclonal antisera to distinguish between species based on unique structural domains of serum proteins has been utilized by the forensic community since the turn of the century. In current forensic practice tests employing such methods as immunoprecipitation, antibody coated latex spheres, or immunodiffusion rely on high quality, carefully tested antisera which have been extensively cross absorbed to eliminate cross reactivity. Such cross reactivity of polyclonal antisera with serum proteins of closely related species is the major limitation of current tests for species of origin in the forensic art. Depending on the discriminatory capability of the polyclonal antiserum in a given method, the phylogenetic relationships between related species impose intrinsic limits on the ability to differentiate related blood or tissue specimens. As Sensabaugh has noted, medico-legal tests would be far more satisfactory if monospecific antisera to rapidly evolving (widely divergent) blood marker proteins were employed, thereby taking advantage of greater differences in the structure of similar proteins, even in closely related species.
Serum albumin has such a potential to be a forensic marker protein because it shows considerable phylogenetic divergence as evidenced by both amino acid sequence data and immunological cross reactivity. Albumins from thousands of pairs of vertebrate species have been compared immunologically and the results have been used to establish approximate time scales for genealogical trees by which these species are related, thereby permitting a quantitative approach to the study of evolution.
A vast literature which spans three decades has demonstrated that serum albumin is a multideterminant antigen.
Recent studies using monoclonal antibodies produced to bovine serum albumin have shown a minimum of 25 different determinants to be present in a panel of 10 mammalian albumins.
At least 13 of these epitopes are non overlapping determinants which are not repeated on subdomains of the albumin molecule. This evidence for the existence of multiple determinants on the albumin molecule provides the rationale for use of monoclonal antibodies to human serum albumin for identification of human tissue and blood in forensic studies.